1. Field of the Invention
The present invention relates to a main steam system around a nuclear reactor.
2. Prior Art
A conventional main steam system around a nuclear reactor in a nuclear power plant is shown in FIG. 5 to FIG. 8. In the conventional main steam system around the nuclear reactor, steam separators 3 and steam dryers 2 are arranged inside a reactor pressure vessel 1 in order to separate a steam-water mixed flow flowing out of a reactor core 4 into steam to be fed to a steam turbine and water to be recirculated into the reactor core 4, as shown in FIG. 5 and FIG. 6.
Among these core internals, the steam dryer 2 includes a plurality of corrugated plates 9 which are aligned parallel to each other to form steam passages between the corrugated plates 9, as shown in FIG. 7. Since the steam flows along the corrugated plate to change the flow direction many times while passing through the gap between the corrugated plates 9, moisture contained in the steam is removed every flow direction change. After that, dry steam obtained by removing moisture from the steam flows out of a steam outlet face 11 of the steam dryer 2 to an upper dome of the reactor pressure vessel 1, and then, the dry steam flows out of the reactor pressure vessel 1 to be conducted to a steam turbine through four main steam nozzles 5 and main steam pipes 6. The flow of the steam inside the steam dryer 2 at that time is shown by hollow arrows in FIG. 8.
On the other hand, the four main steam nozzles 5 are arranged at positions symmetrical with respect to a plane which is parallel to the steam outlet faces of the steam dryers 2 and passes the center of the reactor pressure vessel 1. Further, each of the steam outlet faces 11 of the steam dryers 2 is arranged so as to face the side of the center of the reactor pressure vessel 1, as shown in FIG. 5.
Furthermore, a plurality of main steam safety relief valves 7 for moderating abnormal pressure rise in the reactor pressure vessel 1 are distributively arranged along each of the four main steam pipes 6. The main steam safety relief valve 7 is closed during normal operation of the reactor. However, when pressure in the reactor pressure vessel increases and reaches a set pressure of the main steam safety relief valves 7, the main steam safety relief valves 7 are opened in order to secure safety by relieving steam inside the reactor pressure vessel to the outside of the reactor pressure vessel.
In order to secure the safety in a short time, a plurality of main steam safety relief valves such as those disclosed, for example, in Japanese Patent Application Laid-Open No. 11-14787 are arranged in each of four main steam pipes connected to a reactor pressure vessel, as disclosed in Japanese Patent Application Laid-Open No. 2001-4788.